This invention relates to a magnetron, and more particularly to an improved construction of the filament assembly of a large power magnetron having a ceramic-metal envelope.
Magnetrons are used as ultra-high frequency oscillators for use in microwave ovens or the like. Usually, in the case of industrial microwave ovens, the magnetron is capable of generating useful continuous radio frequency (rf) power in the range of 10 to 30 kilowatts (kw) at very high efficiency. The RCA 8684 Large Power Magnetron shown as 10 in FIG. 1 is an example of such a prior art magnetron which is useful as a 915-MHz, 30 kw rf power source in industrial processing applications. In the operation of such a magnetron it is important that the temperature of any external part of the tube should not exceed certain design limits which are in the range of 100.degree. C. maximum for the metal surfaces and 150.degree. C. maximum for the ceramic insulators. Since the filament current during typical operation is in the range of about 100 amperes at a filament voltage in excess of about 10 volts, external forced air cooling of the filament-cathode terminal contact surface 14 and the filament terminal contact surface 16 is required for safe operation. Since the terminal contact surfaces 14 and 16 are formed by nesting together cylindrical or cup-shaped metal flanges of the filament assembly, electrical connections between an external filament power supply (not shown) and the cylindrical terminal contact surfaces 14 and 16 are made by means of dissimilar coaxial connectors (not shown) secured to the contact surfaces. The coaxial connector which attaches to the filament terminal contact surface 16 also provides an air intake port for directing the air flow around the contact surface 16. This connector is designed to exhaust the air flow toward the filament-cathode terminal contact surface 14 to provide cooling thereto. The coaxial connector which attaches to the filament-cathode terminal contact surface 14 includes a molded rf suppressor to reduce rf leakage. Both of the coaxial connectors described above are extra accessories that increase the cost of the magnetron and make mounting of the magnetron into the equipment unnecessarily complex and time consuming.